1. Field of the Invention
The present invention relates in general to an image scanner of low manufacturing cost and high scanning quality.
2. Description of the Related Art
Generally speaking, flat bed type image scanners are classified into two different kinds in accordance with their different operation ways: reflection-type scanners and transmission-type scanners. The reflection-type scanners are used for scanning non-transparent media such as paper, objects and books. On the other hand, the transmission-type scanners are used for scanning transparent media such as films and slides.
The present invention is related to the transmission-type scanners. Conventional transmission-type scanners include two kinds of light sources: movable and fixed. FIG. 1 is a schematic diagram of a conventional transmission-type scanner provided with a movable light source, wherein a tubular lamp 11 and an optical module 14 are simultaneously moved to scan a transparent object 12 disposed on a piece of glass 13. The image of the transparent object 12 is focused on a charge-coupled device (CCD) 15 contained in the optical module 14. Such a scanner can be put into practice in various ways. For example, what is disclosed in Taiwanese Patent No. 311791.
In the above example, the distribution of intensity of illumination of the tubular lamp 11 is very concentrated, as shown in FIG. 2. If at any moment the movement of the optical module 14 and that of the tubular lamp 11 are not simultaneous, then the light received by the charge-coupled device 15 will be greatly reduced. Thus, the resultant image signal obtained from the charge-coupled device 15 is poor. Therefore, the movement of the optical module 14 and that of the tubular lamp 11 should be always kept simultaneous during the scanning process. However, the tubular lamp 11 and the optical module 14 generally are driven by different mechanisms so that keeping the tubular lamp 11 and the optical module 14 simultaneous is pretty complicated and difficult.
FIG. 3 depicts a conventional scanner provided with a fixed light source, where the light source is a planar light source 31 disclosed in, for example, Taiwanese Patent No. 292032. The planar light source 31 includes two tubular lamps 311, a reflection sheet 315, a lighting guide 317 and a diffuser 316. The reflection sheet 315 is provided on the top of the planar light source 31 to reflect the light of the tubular lamps 311. The lighting guide 317 is used to uniformly distribute the light reflected by the reflection sheet 315 via a plurality of light-guiding dots 318 provided thereon. The diffuser 316 is also utilized to uniformly distribute the light reflected by the reflection sheet 315. Both the lighting guide 317 and the diffuser 316 are of great size. In operations, the planar light source 31 is stationary while an optical module 34 is moved to scan a transparent object 32 disposed on a piece of glass 33. The image of the object 32 is focused on a charge-coupled device (CCD) 35 contained in the optical module 34.
Due to the use of the reflection sheet 315, diffuser 316 and lighting guide 317, the distribution of intensity in this example is much more uniform than that of the previous example. Nevertheless, the intensity difference between the middle and sides of the planar light source is 5%-10% that does not satisfy the requirement for a scanner of high revolution. In addition, forming light-guiding dots 318 on the lighting guide 317 is labor consuming. The greater size of the lighting guide 317 is, the more light-guiding dots 318 are required; thus, the manufacture of lighting guides is difficult and expensive.
An object of the present invention is to provide a scanner that solves the above-mentioned problems.
In accordance with the object of the present invention, an image scanner comprising an image pick-up device and a planar light source is provided. Backlight is generated by the planar light source to transmit through a transparent object. The image pick-up device is used to retrieve the image of the transparent object, i.e., the image of the transparent object is focused on the image pick-up device. In scanning operations, the planar light source and the image pick-up device are simultaneously moved to scan the transparent object.
As described above, the planar light source of the present invention is moved to project backlight onto the simultaneously moving image pick-up device. Accordingly, the size of the planar light source can be small. A lighting guide in the planar light source is also of small size and has fewer light-guiding dots provided thereon; thus, manufacture of the lighting guide of the present invention is easier than that of the prior art. In addition, the distribution of light intensity in the present invention employing the small lighting guide is more uniform than that in the prior art employing the large lighting guide. The difference between the illumination on the middle of the transparent object and the illumination on the sides of the transparent object is less than 1% in the present invention, that is superior to 5%-10% in the prior art. Therefore, the scanning quality of the present invention is superior to that of the prior art.